The present invention relates to a method and apparatus for processing liquid solutions or suspensions in order to reduce the concentration of a substance dissolved and/or suspended therein. The invention could be used in many diverse industrial processes, e.g., for purifying waste solutions, or for extracting specific solutes from solutions or suspensions. The invention, however, is particularly useful in the desalination of saline water, and is therefore described below with respect to such application.
The invention is particularly applicable to industrial processes utilizing a reverse osmosis technique. In the reverse osmosis process, mechanical pressure is applied to the feed liquid on one side of a semipermeable body, such as semipermeable membrane, to force the solvent (e.g., water) through the pores of the semipermeable body while the solute is rejected because of its inability to pass through such pores. Many such semipermeable membranes have been designed for use in reverse osmosis processing, but all are characterized by having small pores in order to pass water molecules while rejecting the salt molecules. Such membranes therefore exhibit very large resistance to the flow of the water molecules through the membrane, and accordingly require extremely high pressures to be used, up to about 70 atmospheres. Further, the resulting throughput of pure water is limited even when large mechanical pressures are applied. Still further, since the pores of the semipermeable membranes must be of relatively small size they are easily clogged, thereby seriously limiting the useful life of such membranes before cleaning or replacement is required. All the foregoing drawbacks of the existing reverse osmosis techniques substantially increase the cost of using reverse osmosis particularly in the desalination of saline water.